As a recording/reproducing head of a hard disk device, a thin film magnetic head that is made with a multilayer film is known. For a thin film magnetic head, in order to meet the advancement of high recording density, a current perpendicular to the plane (CPP)) element in which a sense current flows in the direction perpendicular to a film surface is used. As this type of element, a tunnel magneto-resistance (TMR) element utilizing a TMR effect and a CPP-giant magneto resistance (GMR) element utilizing a GMR effect are known.
As an example of a GMR element or a TMR element, an element provided with a spin-valve film (hereinafter SV film) is well-known. The SV film has a magnetization pinned layer of which a magnetization direction is pinned with respect to external magnetic fields, a magnetization free layer of which the magnetization direction changes according to external magnetic fields and a spacer layer that is positioned between the magnetization pinned layer and the magnetization free layer. The magnetization pinned layer is magnetized in the direction perpendicular to an air bearing surface. A bias magnetic field application layer is disposed at a side of a SV film to apply bias magnetic fields to the magnetization free layer. When the magnetization free layer is not affected by external magnetic fields, the magnetization free layer is magnetized by a bias magnetic field in the track width direction perpendicular to the magnetization direction of the magnetization pinned layer. In order to get good output and SN ratio, it is desirable that the external magnetic field is applied under such a state and the magnetization direction of the magnetization free layer rotates. Under the initial state, when the magnetization direction of the magnetization pinned layer doesn't correspond to the direction perpendicular to the air bearing surface, the output and the SN ratio get worse.
The magnetization direction of the magnetization pinned layer is fluctuated by various factors, especially by heat. A representative process from which the magnetization pinned layer receives heat is an annealing treatment in a wafer process. In recent years, while a high recording density of a magnetic disk is further advancing, in order to increase a recording density in the track width direction, the dimension of the SV film in the track width direction and the volume of the magnetization pinned layer tend to be reduced. In such a magnetization pinned layer with a small volume, the fluctuation of the magnetization direction easily becomes large under the high temperature environment.
In US 2008/0239582, in order to suppress the fluctuation of the magnetization direction of the magnetization pinned layer, a configuration is proposed. With the configuration, a product of a saturation magnetostriction constant of a magnetization pinned layer and an internal stress (a tensile stress is positive) of a pair of bias magnetic field application layers configured with a hard magnetic body is negative. When a pair of bias magnetic field application layers is maintained under the compression stress, the magnetization pinned layer sandwiched between these bias magnetic field application layers stretches in the direction perpendicular to the air bearing surface. The saturation magnetostriction constant is positive. Therefore, the magnetic field in the direction perpendicular to the air bearing surface is induced in the magnetization pinned layer, and the magnetization direction of the magnetization pinned layer is stabilized to the direction perpendicular to the air bearing surface.
When magnetic information is read from a magnetic disk that has a high recording density in the track with direction, the thin magnetic film head easily detects magnetic fields from bits adjacent in the track width direction to the bit that is the reading object. In order to solve such a problem, in US2012/0087045, US2012/0087046, and US2012/0250189, a configuration using a bias magnetic field application layer that includes a soft magnetic layer is proposed. The soft magnetic layer also functions as a magnetic shield (a side shield) to shield external magnetic fields. Therefore, the effect of magnetic fields from adjacent bits in the track width direction can be effectively suppressed.
However, under the high temperature environment, the stress state of the soft magnetic layer is easily changed. Even though an internal stress of a bias magnetic field application layer is a compression stress at the time of the film formation, the internal stress is easily changed into a tensile stress after the bias magnetic field application layer is put under the high temperature environment. When a pair of bias magnetic field application layers is under a tensile stress state, the magnetization pinned layer sandwiched between these bias magnetic field application layers shrinks in the direction perpendicular to the air bearing surface, and the magnetic field in the track width direction is induced. Therefore, the magnetization direction of the magnetization pinned layer becomes unstable.
The purpose of the present invention is to provide the thin film magnetic head that is provided with a spin-valve film that includes a magnetization pinned layer and side layers that include soft magnetic layers to apply bias magnetic fields, and in which the magnetization direction of the magnetization pinned layer of the thin magnetic head is stabilized in the direction perpendicular to the air bearing surface.